External fixation and skeletal immobilization was first described by Boehler, who popularized this technique using pins and plaster in 1929. In 1944, Roger Anderson and Gordon O'Neil introduced the concept of external fixation using an external frame to hold skeletal fixation pins rather than plaster. These fixators are used for comminuted unstable distal radius fractures, both with and without internal fixation of the fracture fragments themselves. External fixation is generally indicated for fractures that have comminution and that are unstable. The rationale for this approach is that the unstable fracture tends to displace despite external support, if the dorsal bone fragments cannot be locked into some semblance of stability. With the palmar fracture line acting as a fulcrum, the compressive force acting along the radial articular surface favors redisplacement. If the applied tensile forces provided by an external fixator can be incorporated across the wrist, this tendency to angular compressive displacement will be minimized.
External fixation can be accomplished with the pins and plaster technique more recently described by Green in his paper, "Comminuted Fractures of the Distal End of the Radius." Green reported excellent results in seventy-five comminuted distal radius fractures treated by this method. Other methods include several available external fixators.
The use of external fixators for the treatment of unstable and comminuted intra-articular distal radius fractures is well established as noted by W. P. Cooney in his paper "External Pin Fixation for Unstable Colles Fractures" as well as Grana and Kopta in their paper, "The Roger Anderson Device and the Treatment of Fractures of the Distal End of the Radius."
Current designs include both static models which hold the fracture in a stable position and dynamic external fixators which allow for some movement. The advantages of external fixators over the pins and plaster technique are facilitation of pin care, absence of constricting casts, lighter weight and ease of wound care; and for dynamic external fixators, wrist motion is allowed while maintaining traction at the fracture site. This last feature is important as wrist motion has been shown to improve the functional results in intra-articular fractures. This was suggested in the papers by Nakata et al., "External Fixators With Wrist Fractures: A Biomechanical and Clinical Study" as well as Salter et al., "The Biological Effects of Continuous Passive Motion on the Healing of Defects in Articular Cartilage."
Generally, fixators employ the principal of longitudinal traction applied to the skeleton by proximal and distal pins at either end of the bone which is fractured. In the case of the wrist, this occurs across the wrist joint, with proximal pins in the radial shaft and distal pins in the metacarpal bones. The benefits to be gained by dynamic external fixators is to allow the combination of stability of the distal radius fracture while allowing freedom of movement of the joint itself. This procedure allows earlier recovery from the stiffness normally associated with immobilization of the fracture while maintaining adequate alignment of the bony fracture itself during the process of healing.
Ideally, the external fixator used in the treatment of comminuted intra-articular fractures of the distal radius should have sufficient rigidity to maintain length and reduction of fracture fragments while allowing motion at the wrist joint. Allowing motion of the wrist and digits after the treatment of distal radius fractures, often with the calculated risk of some loss of reduction, has been advocated especially by Lidstrom in his paper entitled, "Fractures of the Distal End of the Radius: A Clinical and Statistical Study of End Results."
Although a number of prior art dynamic external fixators have been proposed, the dynamic external fixator of the present invention represents a substantial and fundamental advance over prior art devices in that it recognizes that the range of motion defined by the device should precisely correspond to the normal kinematic motion of the wrist. Normal kinematic motion of the wrist is described for example, by Youm and Flatt in their paper, "Kinematics of the Wrist I: An Experimental Study of Radial Ulnar Deviation and Flexion-Extension." According to a preferred embodiment, the present invention does not allow movement which deviates from the normal kinematic movement of the wrist. Furthermore, in order to promote healing, the device of the present invention may be adjusted to limit the range of motion to a portion of the full range of motion of the human wrist. These and other advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiment.